1. Field of the Invention
The present invention relates to an electric power cable line.
2. Description of the Related Art
One of known electric power cable lines which are commonly in use is illustrated in FIG. 1. Shown are power cables 10, straight joints 28 for jointing two cables to each other, terminal ends 29, straight joint constructions 30, and terminal end constructions 31.
FIG. 2 is a longitudinal cross sectional view of the cable 10, in which there are provided a center conductor 12, an inner semiconductive layer 14, a cable insulating layer 16, an outer semiconductive layer 18, a shield layer 20, and a sheath 22. FIG. 2 illustrates an upper half of the cable 10 for simplicity because two, upper and lower, halves of the cable 10 are symmetrical about the axis. FIG. 3 is a schematic view of the straight joint construction 30 showing a joint box 31, an epoxy unit 32, a premolded stress relief cone 34, a retainer 36, and a conductive connector 38.
It is essential for the electric power cable line to withstand a high voltage in long-time service. It is common for the dielectric strength of the straight joints and terminal ends in a long-time supply of high voltage to be as low as about 60% of that of the cable. To increasing the operational reliability of the cable lines, improved straight joints and terminal ends are much desired.